Many types of devices are available to assist a user's breathing, for example when the user is suffering from chronic obstructive pulmonary disease. Often, it may be desirable to apply a positive pressure during an inhalation sequence so as to assist the user when inhaling. At the same time, it may be desirable to provide positive expiratory pressure (PEP) during exhalation, for example to promote alveolar recruitment, reduce dynamic hyperinflation and prevent small airway and alveolar collapse. Typically, however, such benefits are achievable only through the use of expensive, non-portable equipment such as ventilators, bi-level positive airway pressure systems (BPAP) and/or continuous positive airway pressure systems (CPAPS). In addition, these types of devices typically use external pressure sources, for example supplemental oxygen and compressors, to provide pressure support, making them bulky and non-self sustaining.